1. Field of the Invention
The present invention relates generally to computerized methods for accessing synchronized data sets, and in particular, to resolving long-busy conditions for synchronized data sets.
2. Description of Related Art
It is well known in the art to use database management systems, such as IBM""s IMS(trademark) (Information Management System) database management system (DBMS), to manage computerized databases. Indeed, IMS(trademark) has been used for decades and remains in use today.
To enhance performance and database integrity, IMS(trademark) supports the use Multiple Area Data Sets (MADS). MADS are comprised of multiple synchronized copies of the same Area Data Set (ADS) stored on multiple data storage devices. Generally, each ADS is read in a xe2x80x9cround-robinxe2x80x9d fashion to enhance performance, but all ADS""s are written at the same time, to ensure synchronization among the multiple ADS""s.
IMS(trademark) Fast Path (FP) is a set of functions used by application programs that require good response time characteristics and that may have large transaction volumes. IMS(trademark) FP provides these application programs with rapid access to main-storage databases and to direct-access data entry databases. In IMS(trademark) FP, message processing is grouped for load balancing and synchronized for database integrity and recovery.
With MADS, an IMS(trademark) FP I/O operation is performed to every data storage device having an ADS and completion is confirmed to every data storage device before the IMS(trademark) FP I/O operation itself is considered completed. Problems sometimes arise, however, when a data storage device takes too long to perform error recovery. This so-called xe2x80x9clong-busyxe2x80x9d condition might range from couple of seconds to several minutes. This can cause serious problems for an application program that has to remain in a wait-state for an I/O operation until the long-busy condition is resolved.
One solution is to time I/O operations to the data storage device. In this scenario, if a maximum acceptable duration of an I/O operation is exceeded, then the I/O operation is terminated and the data storage device is identified as unavailable. However, identifying the data storage device as unavailable could affect other application programs and the data storage device may have to be manually recovered.
Generically speaking, this problem exists for any higher level I/O operation used to keep multiple copies of data synchronized that directs I/O operations to multiple data storage devices and must have confirmation from all devices before the I/O higher level operation is considered successfully completed. Thus, there is a need in the art for improved techniques for handling long-busy conditions in an online transaction processing or database management system.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method, apparatus, and article of manufacture for resolving long-busy conditions for synchronized data sets. A long-busy condition is detected in a first one of the synchronized data sets. Further access to the first data set is prevented and all subsequent accesses are directed to another, available, second one of the data sets during the long-busy condition. All updates that are made to the second data set during the long-busy condition are identified and stored in a data structure. An untimed read operation is used to determine when the long-busy condition has cleared. Once the long-busy condition is cleared, the first data set is placed into a recovery mode, wherein the identified updates are applied to the first data set. During the recovery mode, the first data set is read-inhibited to prevent read accesses thereto, but the first data set is write-enabled to allow write access thereto. Upon completion of the recovery mode, the first and second data sets are re-synchronized and normal processing can resume.
Various advantages and features of novelty, which characterize the invention, are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there is illustrated and described specific examples of an apparatus in accordance with the invention.